1. Field of the Invention
The present invention relates to a multi-piece rim attached to a tire for a construction vehicle or a mining vehicle, and more particularly, for a large-size construction vehicle or mining vehicle.
2. Background Art
Tires for a large-size construction vehicle or mining vehicle are different in rigidity from tires for passenger vehicles, and there are many cases that tires for a large-size construction vehicle or mining vehicle cannot be fitted to single-piece rims. For this reason, multi-piece rims are often used for tires for a large-size construction vehicle or mining vehicle.
The construction of such a multi-piece rim is shown in FIG. 14.
In FIG. 14, a multi-piece rim 100J has a rim base 1, left and right side rings 2, a bead seat band 3, and a lock ring 4.
A range near an end of the rim base 1 where the lock ring 4 is located (right end in FIG. 14) is a so-called gutter band 11. A back flange 12 is formed at the left end of the rim base 1.
In FIG. 14, the construction for attaching the multi-piece rim to the construction vehicle or mining vehicle side (hub) is not shown.
In FIG. 14, air is pumped into the tire and as the air pressure in the tire become higher, the tire inflates toward the directions indicated by arrows Y (both left and right in FIG. 14) and both the left and right side rings 2 and the bead seat band 3 move toward the directions indicated by the arrows Y.
The lock ring 4 is fitted in a groove 11a formed in the gutter band 11 and the gutter band 11 is integral with the rim base 1. Therefore, the lock ring 4 restrains the side rings 2 and bead seat band 3 from moving in a left direction in FIG. 14.
As shown in FIG. 15, the lock ring 4 has elasticity, particularly an elastic repulsive force which acts to contract the inside diameter of the lock ring 4 in the direction indicated by an arrow R in FIG. 15 (inwardly in the radial direction) to the extent that it becomes equal to, or smaller than, the diameter of the groove bottom of the gutter band groove 11a, and the lock ring 4 has one cut 4s. 
If the lock ring 4 does not have an elastic repulsive force which acts to contract inwardly in the radial direction (a direction indicated by arrows R in FIG. 15), the lock ring 4 will be able to slip out of the groove 11a formed in the gutter band 11. By the elastic repulsive force contracting lock ring 4 acting inwardly in the radial direction (the direction indicated by arrow R in FIG. 15), the lock ring 4 is fitted and held in the gutter band groove 11a. 
In some large-size construction vehicles or mining vehicles, each rear wheel uses a tire assembly which is referred to as a “double tire”.
FIG. 16 shows an example of a “double tire” which is a construction having a tire and a rim on each of the inner and outer sides.
In FIG. 16, the lock rings 4, which are provided on the inner side (machine and/or vehicle body side, a left side in FIG. 16) and outer side (opposite of the machine body side, a right side in FIG. 16) respectively, are so arranged so that they face each other in between the inner and outer tires. This construction intends to ensure that if one of the lock rings 4 should come off, the tire 6 in which the lock ring 4 has come off is moved so as to let it abut on the other tire 6 in order to prevent the tires 6 and various components of the multi-piece rims from coming off the machine body (such as on a construction vehicle and/or mining vehicle).
In a large-size construction vehicle or mining vehicle, tire rotation is carried out frequently so that the tires 6 wear uniformly and the service life of the tires 6 is extended. If a tire is punctured, the tire 6 must be removed for repair.
For this reason, the frequency of the removal of the tire 6 is higher in a large-size construction vehicle or mining vehicle. In the case of a double tire, it is possible that both the outer tire 6 and the inner tire 6 have to be removed from the machine body.
In case both tires 6 should be removed, in the case of a multi-piece rim 100J in the prior art shown in FIG. 16, it is necessary for removal of the inner tire 6 to remove the outer tire 6 and outer multi-piece rim 100J from the machine body.
The multi-piece rim 100J shown in FIG. 16 has the back flange 12 outside the outer rim base (right side in FIG. 16). Therefore, in case that the outer tire 6 should be removed from the rim base 1, first the radial inner edge of the tire 6 is interfered with by the side ring 2, and then, the side ring 2 is interfered with by the back flange 12 or a radial projection (a lip, not shown in the figure) at an end of said back flange.
Therefore, in the case shown in FIG. 16, it is impossible to remove only the outer tire 6 toward the outer side (a right side in FIG. 16) of the rim base 1.
Also, in case that there are the back flange 12 and lip thereof (not shown) in the outer multi-piece rim 100J, even if the inner tire 6 should be removed, said inner tire is interfered with by the back flange 12 and lip thereof (not shown) and cannot be removed from the machine body.
In the prior art shown in FIG. 16, in order to remove the outer multi-piece rim and tire from the machine body, it is necessary to remove bolts B1 from the hub 5, and to remove the outer tire 6, the rim base 1 and a fitting member 7 (member for fitting the rim base 1 to the hub) from the hub 5 in a state that the outer tire 6, the rim base 1 and a fitting member 7 are combined.
However, for example, the number of bolts B1 is 50-70. Although there are cases that the number of bolts B1 is smaller than that example, considerable labor is required to remove a relatively large number of bolts B1 (in some cases, a great many bolts B1 should be removed).
A technique shown in FIG. 17 has been proposed, in order to solve the problem in the prior art shown in FIG. 16, that is, the outer multi-piece rim must be removed from the machine body for removing the inner or outer tire 6.
In FIG. 17, one multi-piece rim 100 (outer multi-piece rim) includes two side rings 2, two gutter bands 11, two bead seat bands 3, and two lock rings 4. Therefore, in the prior art shown in FIG. 17, there is no back flange 12 which is shown in FIG. 16 on the outer side.
Therefore, the inner tire 6 and outer tire 6 can be pulled out toward the direction indicated by an arrow Y in FIG. 17 in a state that the rim base 1 is fitted to the hub 5, without removing the rim base 1 of the multi-piece rim 100 from the machine body.
However, in the multi-piece rim 100 shown in FIG. 17, in a case that the lock ring 4 of the prior art as shown in FIG. 15 is applied, when attaching the lock ring 4 to the outer multi-piece rim or inner multi-piece rim, the lock ring 4 must be passed through the rim base 1 of the outer multi-piece rim 100 and be fitted into the groove 11a of the gutter band 11, while the radial dimension (a dimension in the direction indicated by R in FIG. 15) of the lock ring 4 is held large against the elastic repulsive force (the elastic repulsive force which contracts the ring toward the direction indicated by arrow R).
For example, there are cases that the mass of the lock ring 4 is 50 kg or so, it would be very difficult and require a great deal of labor to place such a heavy lock ring 4 in a prescribed position while holding it against the elastic repulsive force which contracts said lock ring inwardly in the radial direction.
On the other hand, instead of the one-piece lock ring shown in FIG. 15, a two-piece lock ring has also been proposed.
In the prior art in which a two-piece lock ring is used, after such a lock ring (a lock ring being divided in two portions) is fitted into the groove 11a (FIG. 14) of the gutter band 11 and held in the so-called “locked” state, where both ends of the half portions are coupled (fastened) by means of fasteners such as screws and plates.
By such construction in which both ends of the half lock ring portions are coupled by fasteners, the lock ring is securely fitted in the groove 11a (FIG. 14) of the gutter band 11, and therefore, the elastic repulsive force, which contracts the lock ring inwardly in the radial direction, is not necessary.
However, in the two-piece lock ring of the prior art, there are following problems.
First, in a process for coupling the lock ring, each half portion of the lock ring must be securely fitted in the groove 11a of the gutter band (such that the half portions must be in a “locked” state).
Because, in case that the half portions of the lock ring are coupled by means of fasteners in a state that said portions are not properly fitted in the groove of the gutter band (see 11a in FIG. 14), it is difficult to combine the multi-piece rim 100 with the tire 6 accurately (to combine the multi-piece rim 100 with the tire 6 is a so-called “assembly”).
Second, if the tire diameter is large, the lock ring mass must be correspondingly large. Therefore, a large amount of labor is required to support the lock ring so as to securely fit each half portion of the lock ring in the groove of the gutter band (see 11a in FIG. 14).
Specifically, in some cases, two or more workers are needed and a machine for supporting each half portion of the lock ring must be prepared.
Third, if the lock ring is divided in two portions, the number of components to be managed (components under management) should be increased.
Fourth, since the lock ring is divided in two portions, coupling work (fastening work) has to be carry out at two points for one lock ring. Thus the number of needed tasks is increased.
As another prior art, a multi-piece rim disk wheel has been proposed in which a rim base is joined with a gutter band, first and second center bands, a disk and a back flange by complete penetration butt-welding to cope with an increase in payload (see Patent Document 1).
Such a prior art reference is useful but does not solve the problem caused by applying a two-piece lock ring as mentioned above.
Patent Document 1:
Japanese non-examined Patent Publication No. 2000-108603